Forming heaters for phase change memories

ABSTRACT

A heater for a phase change memory may be thrilled by depositing a first material into a trench such that the material is thicker on the side wall than on the bottom of the trench. In one embodiment, because the trench side walls are of a different material than the bottom, differential deposition occurs. Then a heater material is deposited thereover. The heater material may react with the first material at the bottom of the trench to make Ohmic contact with an underlying metal layer. As a result, a vertical heater may be formed which is capable of making a small area contact with an overlying chalcogenide material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of pending U.S. patent application Ser.No. 12/944,134, filed Nov. 11, 2010, which application is incorporatedherein by reference, in its entirety, for any purpose.

BACKGROUND

This relates generally to phase change memories. Phase change memoriesuse a chalcogenide layer that changes phase between more amorphous andless amorphous or more crystalline phases. Generally, the phasetransition is the result of Joule heating of the chalcogenide layer. Insonic cases, the heating of the chalcogenide layer is due to electricalheating through a heating element proximate to the phase change materiallayer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged, partial, cross-sectional view alone embodiment ofthe present invention at an early stage;

FIG. 2 is an enlarged, cross-sectional view at a subsequent stageaccording to one embodiment;

FIG. 3 is an enlarged, cross-sectional view at still a subsequent stagein accordance with one embodiment;

FIG. 4 is an enlarged, cross-sectional view at a subsequent stage inaccordance with one embodiment;

FIG. 5 is an enlarged, cross-sectional view at a subsequent stageaccording to one embodiment; and

FIG. 6 is an enlarged, cross-sectional view at a subsequent stageaccording to one embodiment.

DETAILED DESCRIPTION

In accordance with some embodiments, differential deposition can be usedto form vertical high aspect ratio heaters for phase change memories.The vertical heaters may be more effective because they have a smallerpoint of contact with the chalcogenide material, that point of contactdetermined h the thickness in the horizontal dimension of the phasechange material heater, which is deposited as a layer in the verticaldirection.

Therefore, the heater can have a critical dimension thinner than anythickness possible with lithographic techniques. As a result of the thinarea of contact between the heater and the phase change material layer,less material in the phase change layer must be required to change phaseand, therefore, less energy is needed to make the phase transition. As aresult, power consumption may be improved in some embodiments.

Referring to FIG. 1, in some embodiments, a vertical wall dielectric 14may be formed. In some cases, the dielectric 14 may be formed with atrench, Figure I only showing the left side of a trench. The dielectric14, in one embodiment, may be stacked oxide and nitride layers. However,any dielectric may be utilized. The dielectric 14 is formed on top of ametal layer 12 which acts as to conductor lower electrode, or addressline.

In some embodiments, a deposition technique is used to form a layercomposed of a thicker vertical portion 16 on the dielectric 14 and athinner horizontal portion 18 on the metal 12. The difference indeposition thickness is the result of the differential deposition thatoccurs on metal, compared to dielectric materials. Specifically, withsome deposition processes, such as atomic layer deposition, morematerial is deposited on dielectrics than on metals. For example, in aflow of boron B₂H₆, the boron is well physisorbed on an oxide/nitridelayer 14 and less effectively physisorbed on metals, resulting indifferential thicknesses. Another technique that can be utilized is SiH₄deposition, however, the film performance may not be as good as thatachieved with boron.

Next, a heater material 20 is deposited, as indicated in FIG. 2, using adeposition technique, such as atomic layer deposition. For example, theatomic layer deposition of tungsten may he used to form the heatermaterial 20 which has a vertical portion and a horizontal portion 22.However, the horizontal portion 18 on the metal 12 is consumed duringthe heater material 20 deposition process As a result, physical contactis achieved between the heater material 20 and the metal 12. Next, tosecond boron layer may be deposited, again, using B₂H₆ flow, in oneembodiment, to form the capping layer 24, as shown in FIG. 3. Again,atomic layer deposition may be used, for example.

More specifically, the reason for the consumption of the baron formingthe horizontal portion 18 at the bottom of the trench is that tungstenfluoride (WF₆) reacts with any boron at the metal surface, achievingOhmic contact to the metal surface, Good adhesion between the tungstenbased layer and the dielectric 14 is guaranteed by the residual of borondeposited on the dielectric and still remaining on the dielectric 14.The second B₂H₆ atomic layer caps the in situ heater material 20.

Next as shown in FIG. 4, a dielectric layer 26 is blanket deposited overthe structure and then planarized down to the upper surface 28 of thedielectric 14, as shown in FIG. 5,

Finally, a chalcogenide layer 30 is deposited, as indicated in FIG. 6.The vertical heater material 20 makes a small area or point contact withthe chalcogenide layer 30. Thereafter, the chalcogenide layer may becovered with additional layers, including another electrode or metallayer (not shown). Then, additional layers (also not shown may bedeposited, such as the layers forming an ovonic threshold switch, as oneexample. In some embodiments, the surface area of contact between thevertically oriented heater material 20 and the chalcogenide layer 30 isgoverned by the thickness of the deposition of the heater material 20.Using atomic layer deposition, this layer can be made extremely issmall, resulting in a very small area of contact between thechalcogenide layer 30 and the heater material 20.

While the figures depict the formation of the single cell, a largenumber of cells may be formed at the same time, for example, by forminga plurality of spaced trenches in a dielectric 14. Then, in each trench,the layers shown in FIGS. 1-6 may be deposited and processed in thefashion indicated. As a result, a number of cells may be formed,initially, with a common chalcogenide layer 30. In some embodiments, thechalcogenide layer may then be singulated so that the chalcogenide layeris no longer continuous across the plurality of cells, but is distinctand constitutes a dot at each cell. Thus, a plurality of cells may beformed along a line, defined by the metal 12 and perpendicular lines maybe defined by conductors extending transversely to the length of themetal 12, contacting the upper surface of the chalcogenide 30 after ithas been singulated.

Programming to alter the state or phase of the material may beaccomplished by applying voltage potentials to the address lines,thereby generating a voltage potential across a memory element includinga phase change layer 30. When the voltage potential is greater than thethreshold voltages of any select device and memory element, then anelectrical current may flow through the phase change layer 30 inresponse to the applied voltage potentials, and may result in heating ofthe phase change layer 30 through the action of the heater 20.

This heating may alter the memory state or phase of the layer 30, in oneembodiment. Altering the phase or state of the layer 30 may alter theelectrical characteristic of memory material, e.g., the resistance orthreshold voltage of the material may be altered by altering the phaseof the memory material. Memory material may also be referred to as aprogrammable resistance material.

In the “reset” state, memory material may be in an amorphous orsemi-amorphous state and in the “set” state, memory material may be in acrystalline or semi-crystalline state. The resistance of memory materialin the amorphous or semi-amorphous state may be greater than theresistance of memory material in the crystalline or semi-crystallinestate. It is to be appreciated that the association of reset and setwith amorphous and crystal line states, respectively, is a conventionand that at least an opposite convention may be adopted. Usingelectrical current, memory material may be heated to a relatively highertemperature to melt and then quenched to vitrify and “reset” memorymaterial in an amorphous state (e.g., program memory material to a logic“0” value). Heating the volume of memory material to a relatively lowercrystallization temperature may crystallize or devitrify memory materialand “set” memory material (e.g., program memory material to a logic “1”value). Various resistances of memory material may be achieved to storeinformation by varying the amount of current flow and duration throughthe volume of memory material.

References throughout this specification to “one embodiment” or “anembodiment” mean that a particular feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneimplementation encompassed within the present invention. Thus,appearances of the phrase “one embodiment” or “in an embodiment” are notnecessarily referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be instituted inother suitable forms other than the particular embodiment illustratedand all such forms may be encompassed within the claims of the presentapplication.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

What is claimed is:
 1. An apparatus comprising: a substrate; a verticalwall defined over the substrate: a material formed on the vertical wall;and a heater material including a horizontal portion formed in contactwith the substrate and a vertical portion formed in contact with thematerial.
 2. The apparatus of claim 1, wherein the substrate is formedof metal and the vertical wall is formed in a dielectric.
 3. Theapparatus of claim 2, further comprising a layer of the material formedover the heater material.
 4. The apparatus of claim 1, wherein thematerial includes boron.
 5. An apparatus comprising: a metal material; aheater including a horizontal portion formed adjacent to the metalmaterial and a vertical portion formed between two columns of amaterial, wherein the vertical portion of the heater contacts thematerial of the two columns.
 6. The apparatus of claim 5, wherein thematerial comprises boron.
 7. The apparatus of claim 5, farthercomprising a phase change material defined over the vertical portion andthe two columns of the material.
 8. The apparatus of claim 7, whereinthe phase change material comprises a chalcogenide material.
 9. Theapparatus of claim 7, wherein the phase change material has a firstresistance in a first state and a second resistance in at second state.10. The apparatus of claim 5, wherein the metal material is coupled to aaddress line.
 11. An apparatus comprising: a plurality of phase changememory (PCM) cells, wherein a PCM cell of the plurality of PCM cellscomprises a substrate, a heater, and a chalocogenide material, wherein afirst portion of the heater contacts the substrate and a second portionof the heater contacts the chalcogenide material, wherein the secondportion of the beater is formed between a first layer of a firstmaterial and a second layer of a second material, wherein the secondportion of the heater contacts the first layer and the second layer,wherein the first material and the second material each comprise boron.12. The apparatus of claim 11, wherein the first material is the samematerial as the second material.
 13. The apparatus of claim 11, whereineach PCM cell of the plurality of PCM cells comprises a dot of thechalcogenide material.
 14. The apparatus of claim 13, wherein a firstsubset of the plurality of PCM cells comprises the substrate, whereinthe first subset of the plurality of PCM cells forms a line defined bythe substrate.
 15. The apparatus of claim 14, wherein the substratecomprises a first conductive line.
 16. The apparatus of claim 15,wherein the dot of the chalcogenide material is coupled to a secondconductive line that extends transversely to a length of the firstconductive line, wherein a second subset of the plurality of PCM cellsforms a line defined by the second conductive line that is perpendicularto the first conductive line.
 17. The apparatus of claim 16, wherein thefirst conductive line and the second conductive line each comprise ametallic material.
 18. The apparatus of claim 11, wherein thechalcogenide material of the PCM cell is configured to have a firstresistance in a first state and a second resistance in the second state.19. The apparatus of claim 11, wherein the first layer contacts adielectric material.
 20. A memory cell comprising: a heater between ametal material and a phase-change material, wherein the heater comprisesa vertical portion and a horizontal portion, wherein the horizontalportion of the heater is in physical contact with the metal material,and wherein a layer of a material is between the vertical portion of theheater and a vertical wall.
 21. The memory cell of claim 20 wherein ascontact between the horizontal portion of the heater and the metalmaterial is devoid of the material.
 22. The memory cell of claim 20,wherein the material includes boron.
 23. The memory cell of claim 20,further comprising a capping layer of a second material, wherein thevertical portion of the heater is between the layer of the material andthe capping layer of the second material.
 24. The memory cell of claim23, wherein the vertical portion of the heater contacts the layer of thematerial and contacts the capping layer of the second material.
 25. Thememory cell of claim 23, wherein the material and the second materialeach include boron.